Abstract:

The dynamic response of a two-column bridge pier with an innovative structural frame and flexible footings was studied. The objectives of the study were to determine the effect of footing flexibility, the adequacy of using carbon fiber reinforced fabrics as primary reinforcement, and the performance of bents with shifted plastic hinges in columns. Also, extensive analytical work was performed to formulate a simple method to assess the amount of moment reduction due to footing flexibility.

A quarter-scale bent with two square columns supported on isolated spread footings previously tested on a shake table was the primary subject of the study. The bent was tested in three modes: rocking with as-built footings, rocking with retrofitted footings, and fixed base. The columns were detailed with pre-assigned plastic hinges away from the column ends using a combination of carbon fiber reinforced plastic (CFRP) fabrics and steel. CFRP was used as the shear and confinement reinforcement throughout the entire frame. Analysis of the experimental data revealed that footing flexibility significantly reduced the moments near the base of the frame; however, this reduction became less pronounced as the distance from the footing increased. Using analytical models, design charts were created to assess the amount of moment reduction due to footing flexibility. These charts allow a designer to reduce the moment calculated from a fixed base model. The effectiveness of shifted plastic hinges was evaluated using over-strength ratios and by examining the experimental data. The results showed that shifting of the plastic hinges was effective in localizing the damage away from the column ends. The over-strength ratios and strain data also revealed that the design of the CFRP was a successful replacement to conventional steel reinforcement.